1. Field of the Invention
The present invention relates to dynamic capacitance compensation (DCC) for a liquid crystal display (LCD), and more particularly, to a DCC compensation apparatus and method for an LCD, which can easily process image data in real time, reduce the number of memories, and hardly suffer from degradation of image quality.
2. Description of Related Art
A liquid crystal display (LCD) injects a liquid crystal between two sheets of glass, applies electrical pressure thereto, and displays characters/images using optical changes that occur when the sequence of the crystal liquid molecules is changed by the electrical pressure. LCDs operate on 1.5V-2V and are widely used in watches, calculators, and laptop computers due to low power consumption.
One of the disadvantages of LCDs is slow response time. The slow response time causes values of previous and current images to be combined, resulting in a blurring phenomenon. Generally, one frame lasts approximately 16.7 ms. When voltage is applied to both ends of liquid crystal material, it takes time for the liquid crystal material to respond. Therefore, time delay is required to express a desired pixel value and such time delay causes blurring.
To improve response time of LCDs, a dynamic capacitance compensation (DCC) method is used. In DCC, the difference between a pixel value of a previous frame and a pixel value of a current frame is calculated, a value proportional to the difference to the pixel value of the current frame is added, and the result of addition is outputted. To perform DCC, pixels values of the previous frame must be stored in a memory.
However, a writing memory for storing the pixel values of the previous frame and a reading memory for reading the stored pixel values are required to store the pixel values of the previous frame without compression. In other words, independent writing and reading memories must be installed to smoothly perform the DCC by storing the uncompressed pixel values of the previous frame in the writing and reading memories.
To relieve the burden of having to install two or more memories, compressing image data may be considered. In other words, a bit stream of the pixel values of the previous frame is compressed using an encoder and stored in a memory, and the compressed bit stream is decoded using a decoder. Then, the pixel values of the previous frame are compared with the pixel values of the current frame to perform the DCC.
A color sampling compression method has been used to compress pixel values of a previous frame. In the color sampling compression method, the pixel values of the previous frame are compressed through YcbCr conversion and down-sampling processes. Here, Y denotes luminance, and Cb and Cr denote chrominance. However, the color sampling compression method changes color and has poor compression efficiency.
In this regard, to perform the DCC, conventional LCDs store the pixel values of the previous frame without compression or compress the pixel values of the previous frame through the color sampling compression, running the risk of compromising image quality.